Why a Thermal Scan Belongs in Every Home Inspection

If you own or are buying a home in Seattle, Bellevue, Stanwood, or Tacoma, essentially, Western Washington, a thermal (infrared/IR) scan is one of the most cost‑effective ways to uncover problems before they become expensive repairs. In our marine 4C climate—long wet seasons, short drying windows—small leaks and hidden moisture don’t stay small for long. Seattle alone averages ~39.34 inches of precipitation and ~156 days with measurable rain each year, with November the wettest month. That’s a lot of opportunities for water to find its way in. Wikimedia Commons

TL;DR: A thermal scan during a home inspection helps us pinpoint hidden moisture, missing insulation, and electrical hot spots. In the Seattle–Bellevue–Tacoma area, with frequent rain and wind‑driven moisture, it’s an essential layer of due diligence—not a luxury.

What a Thermal Scan Can Reveal (Real PNW Examples)

• Active or recent moisture intrusion at roofs, skylights, chimneys, decks, and around windows/doors—even when surfaces look normal. IR highlights suspicious temperature patterns we then verify with moisture meters (pin and pinless) so you’re not chasing “ghosts.” InterNACHI+1

• Insulation gaps and air leakage at knee walls, attic hatches, cantilevers, and rim joists—common in older Seattle and Tacoma housing stock—show up as cool streaks in winter or warm bands in summer. We follow ASTM C1060, the industry practice for thermographic inspections of framed buildings. ASTM International | ASTM

• Electrical hot spots (loose lugs, overloaded breakers, oxidized connections) that may not be visible in a standard visual inspection. IR helps us prioritize what needs an electrician under safe, normal load conditions per accepted maintenance guidance. InterNACHI+1

Why IR is Extra Valuable in Seattle’s Rain

• The Puget Sound marine climate (IECC Zone 4C) means long periods of damp weather and limited drying potential; wind‑driven rain is the biggest moisture load on walls and roofs. That’s exactly when IR + moisture metering helps isolate the leak path quickly. Seattle+1

• At Sea‑Tac, normals show ~18 wet days in November and ~6.3 inches of rain on average that month—prime time for maintenance scans to catch flashing failures and siding/window leaks before they spread. Wikimedia Commons

• Rain intensity in Seattle has trended upward in recent decades, increasing flood and leak risks during heavy bursts; proactive envelope checks and well‑maintained drainage matter more than ever. Axios

How a Trained Eye—and the Right Process—Makes the Difference

Not all thermal scans are equal. We don’t just “wave a camera.” We apply repeatable, standards‑based steps so the images tell a true story and not a misleading one.

1. Time it for contrast (ΔT): We aim for a detectable temperature differential (often ~10°F/5–6°C or more) between indoors and outdoors, or use recent rainfall and indoor conditioning to create contrast. Without ΔT, you can misread patterns. IRINFO.ORG Infrared Thermography

2. Calibrate for surfaces: We set emissivity and reflected apparent temperature correctly (glass, metal, and glossy paint reflect IR and can fool the camera). Then we adjust our shooting angle to reduce reflections. FLIR Support

3. Verify, don’t guess: IR can’t “see through walls.” It shows surface temperature patterns. We confirm with moisture meters or other tests before we call a defect. Flir+1

4. Document & prioritize: Findings are captured with visual + thermal images and moisture readings so you (and your contractors) know where to open and what to fix first.

   

Our Tool Stack (Used Properly)

• Professional thermal imagers with adjustable emissivity/reflective settings and focus control (critical for accuracy). Flir Media

• Pin + pinless moisture meters, often integrated with IR to guide exactly where to probe and record readings alongside thermal images. Flir Media

• Electrical IR protocol: We inspect accessible panels under typical operating load and flag anomalies for a licensed electrician, aligning with thermal best‑practice guidance used in NFPA‑70B programs. Fluke Corporation

• ASTM C1060 workflow for building envelope scans to reduce false positives and improve repeatability. ASTM International | ASTM

Local Focus: Typical Issues We Catch Around Seattle, Bellevue & Tacoma

• Window and door leaks from aging sealant or missing head flashing—especially on windward façades that take the brunt of driving rain. Building Science

• Deck ledger & balcony penetrations where flashing laps are backward or missing.

• Siding transitions (stucco/fiber‑cement/cedar) with failed WRB detailing—IR helps target where to open the wall instead of “chasing” a leak.

• Attic condensation at eaves and bath fan terminations during cold snaps.

• Crawlspace moisture and rim‑joist air leakage contributing to musty odors.

• Roof trouble spots that often worsen in our damp climate—IR can help you prioritize repairs before moss and moisture accelerate wear.

Maintenance Inspections in a Rainy Climate: A Smart Seattle‑Area Routine

For Seattle, Bellevue, Tacoma, a sensible maintenance cadence is:

• Pre‑storm season (Oct–Nov): Thermal scan + roof/gutter checks to prep for the wettest months; Seattle’s normals confirm late fall is peak‑risk. Wikimedia Commons

• Late winter/early spring (Feb–Apr): Follow‑up IR if you’ve noticed stains or musty odors; confirm whether winter moisture dried or is still active.

• Keep drainage working: Seattle/King County actively promotes RainWise approaches (cisterns, rain gardens) because big storms can overwhelm systems; proper downspouts and slope away from the home are key. King County

Seattle Rain = Roof & Gutter Vigilance

Moss and continually damp surfaces are part of life here—and part of roof wear. Local university and extension guidance in the Pacific Northwest note that moss thrives in cool, moist, shaded conditions, so trimming overhanging limbs and keeping gutters clear are preventative musts. OSU Extension Service+1

Pro tip: Pair your roof/gutter service with an IR scan during or shortly after a storm—we often catch subtle leaks at penetrations and valleys that are invisible once surfaces dry.

FAQs (Schema‑friendly)

Does IR see through walls?
No. IR detects surface temperature patterns. We verify with moisture meters to confirm any suspected moisture. Flir+1

When is the best time to do an IR scan here?
Before and during the wet season (Oct–Mar) or right after heavy rain, and whenever there’s enough ΔT between indoors and outdoors to highlight anomalies. IRINFO.ORG Infrared Thermography+1

Is Seattle actually a marine climate?
Yes—Seattle is IECC Climate Zone 4C (marine), which influences how buildings get wet and dry. Seattle

Bottom Line

In Seattle, Bellevue, and Tacoma, where rain is frequent and drying time is limited, a thermal scan is one of the most effective ways to find moisture, verify insulation, and flag electrical concerns early. We follow ASTM C1060, calibrate our equipment correctly, and confirm findings with meters so you can act with confidence. ASTM International | ASTM+2FLIR Support+2

Citations (selected)

• Sea‑Tac 1991–2020 normals (precip totals & rainy days). Wikimedia Commons

• Seattle is IECC Zone 4C (marine). Seattle

• Driving rain = major moisture load on walls. Building Science

• IR moisture intrusion (InterNACHI). InterNACHI

• IR electrical inspections (InterNACHI & NFPA‑70B guidance overview). InterNACHI+1

• ASTM C1060 standard (thermographic inspections of framed buildings). ASTM International | ASTM

• IR technique—ΔT, emissivity, reflected temp. IRINFO.ORG Infrared Thermography+1

• Seattle RainWise stormwater context. King County

• Rain intensity trend in Seattle. Axios